Field
The present disclosure relates to telecommunications apparatus and methods. In particular, certain embodiments relate to schemes for communicating allocations of transmission resources of a shared channel in a wireless telecommunications system.
Description of Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Mobile communication systems have evolved over the past ten years or so from the GSM System (Global System for Mobile communications) to the 3G system and now include packet data communications as well as circuit switched communications. The third generation partnership project (3GPP) is developing a fourth generation mobile communication system referred to as Long Term Evolution (LTE) in which a core network part has been evolved to form a more simplified architecture based on a merging of components of earlier mobile radio network architectures and a radio access interface which is based on Orthogonal Frequency Division Multiplexing (OFDM) on the downlink and Single Carrier Frequency Division Multiple Access (SC-FDMA) on the uplink.
Third and fourth generation mobile telecommunication systems, such as those based on the 3GPP defined UMTS and Long Term Evolution (LTE) architecture are becoming able to support more sophisticated services than simple voice and messaging services offered by previous generations of mobile telecommunication systems. For example, with the improved radio interface and enhanced data rates provided by LTE systems, a user is able to enjoy high data rate applications such as mobile video streaming and mobile video conferencing that would previously only have been available via a fixed line data connection. The demand to deploy third and fourth generation networks is therefore strong and there is a corresponding desire to extend the coverage available in such telecommunications systems (i.e. there is a desire to provide more reliable access to wireless telecommunications systems for terminal devices operating in coverage-limited locations).
A typical example of a coverage-limited terminal device might be a so-called machine type communication (MTC) device, such as a smart meter located in a customer's house and periodically transmitting information back to a central MTC server relating to the customer's consumption of a utility, such as gas, water, electricity and so on. Such a terminal device might operate in a coverage-limited location because, for example, it may be located in a basement or other location with relatively high penetration loss. Further information on characteristics of MTC-type devices can be found, for example, in the corresponding standards, such as ETSI TS 122 368 V10.530 (2011 July)/3GPP TS 22.368 version 10.5.0 Release 10) [1]. Some typical characteristics of MTC type terminal devices/MTC type data might include, for example, characteristics such as low mobility, high delay tolerance, small data transmissions, infrequent transmission and group-based features, policing and addressing.
In some situations a terminal device in a coverage-limited situation in a particular communication cell served by a base station might be unable to receive communications from the base station unless specific provision is made for it to do so. One way to increase coverage in this situation would be for the base station to increase the power of its transmissions. However, a blanket increase in transmission power from a base station could be expected to give rise to increased interference in neighbouring communication cells. An alternative approach would be for the base station to in effect focus/concentrate its available transmission power budget into a subset of transmission resources (e.g. in terms of frequency) which are selected from within the base station's overall transmission resources and allocated for transmissions to coverage-limited terminal devices. However, this approach can again lead to increased interference in neighbouring cells and may in some cases require increased coordination among base stations to optimise performance.
Another approach for providing coverage extension is to rely on repeated transmissions of signalling in multiple subframes. A terminal device may then combine the signalling received for a plurality of repeated transmissions to increase the likelihood of successfully decoding the signalling, e.g. using chase combining/maximal ratio combining techniques. This repeated transmission approach may be applied for control signalling (e.g. sent on a physical downlink control channel such as PDCCH in LTE) and/or other signalling (e.g. sent on a physical downlink shared channel such as PDSCH in LTE).
One draw-back of a repeated transmission approach for providing coverage extension is a corresponding increase in the amount of transmission resources needed to communicate with terminal devices, particularly in the amount of transmission resources needed to provide control messages to the terminal devices, and the inventors have recognised how this issue can be especially significant for certain types of communications, as discussed further below. There is therefore a need for schemes which can allow for communications with terminal devices to be made over a number of subframes with a reduction in the overall amount of transmission resources needed to support this as compared to conventional techniques.